[quote]On 2 Aug 2008 at 13:56, Ben wrote:
> Most used laptop packs are probably used and abused.. Either the cells are no
> good or (if you believe some websites - may be true) the BMS is cutting back
> on the capacity early.
Maybe. I have a couple of T-model Thinkpads and a 600E. All these are
infamous for battery problems. (My old 760EL ran the original L-Ion battery
for over 10 years, albeit with appreciably reduced capacity toward the end.)
The batteries comprise 6 cells, 2P3S. For some reason, the middle pair of
the three buddy pairs frequently fails first (heat?). The symptom is that
the battery meter on the screen abruptly drops from 80% or so to 20% or so.
Apparently the BMS monitors the individual pairs, and when the weak pair's
voltage drops, it quickly "corrects" the SOC.
One of the tricks I've read about, but haven't yet tried, is to scrounge the
outer cells from a second allegedly bad battery, and use them to replace the
inner cells.
So, what I'm driving at is the significant possibility that other laptop
batteries are managed the same way -- that is, one or two weak cells might
be limiting the battery's capacity. Thus, it might indeed be possible to
scrounge 50% to 75% usable cells from old laptop batteries.
Now, keep in mind that most of these cells, though still usable, will
already be a good 3-7 years old. Whether you'll get enough life from them
in an EV to make it worth the effort of building a massive pack is quite
another story. If you have more time than money, a ready source of massive
quantities of old laptop batteries, and a means of testing the cells, it
might be worth tinkering with.
David Roden - Akron, Ohio, USA
EVDL Administrator
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[EVDL] Surplus Li ion packs on craigslist
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